This invention relates to an apparatus and method for feeding a metal refining furnace, and more particularly to a continuous feeding or charging mechanism for an electric arc steelmaking furnace.
Generally, the operation of an electric arc steelmaking furnace has been an intermittent operation, wherein the sequence followed is: charging of steel scrap and/or direct reduced iron, pig iron, slag formers and alloying elements; ignition or establishment of an electric arc between the electrodes in the furnace to create melting conditions for melting the charge and forming a molten metal bath covered by a molten slag; refining for a period of time during which the molten metal portion of the bath is refined to form steel having a desired composition and quality; and periodically raising the electrodes to remove them from contact with the bath and interference with the tapping procedure; then tapping the molten metal. In addition, slag can be removed by a slagging, or slag-off, operation as required.
Although this invention is shown and described in connection with an electric arc steelmaking furnace, it will be readily apparent that any electric powered steelmaking furnace, including but without limitation, plasma furnaces, DC furnaces, and induction furnaces, could be substituted for an electric arc steelmaking furnace with similar results. In the steelmaking practice known as "continuous charging" or "continuous melting", charge or feed materials are introduced to a furnace during the charging, melting and refining periods, then charging is interrupted and power input is interrupted for the tapping procedure. In U.S. Pat. No. 4,543,124, issued Sept. 24, 1985, an electric furnace operation was disclosed which allowed continuous operation without interruption of either charging or power input during the tapping procedure.
The procedure described above includes segregating prepared scrap, preheating prepared scrap, then feeding the scrap, direct reduced iron or other charge materials to an electric arc steelmaking furnace. This was accomplished by continuous feed means, disclosed as a charging conveyor which passes through a refractory tunnel, then into the furnace. In order to feed scrap continuously, it is advantageous to charge through the sidewall of the electric furnace. Small particles, such as direct reduced iron can be fed through the furnace roof.
I have invented a method and apparatus for feeding an electric arc steelmaking furnace, which incorporates continuous preheating and feeding, and results in an increase in productivity, and reduced operating costs.
The present invention provides means for charging materials from a conveyor, such as disclosed in U.S. patent application Ser. No. 787,959, filed Oct. 16, 1985, U.S. Pat. No. 4,609,400, into an electric arc steelmaking furnace having a charging opening in its sidewall. The apparatus is a connecting or charging car, which includes a vibrating pan which also acts as a chute within an enclosed chamber, which chamber can function as a combustion chamber. A chute portion of the apparatus protrudes into the furnace sidewall opening, and need not be removed when tilting the furnace for slagging or tapping. The chute and pan are preferably rotatable about a vertical axis through an arc of about 20.degree..
Within the furnace sidewall, and preferably incorporated into the furnace shell, is an inclined furnace feed chute, which further carries feed materials past the sidewall into the furnace.
When connected between a charge preheater and an electric furnace, the charging car chamber functions as a gas-tight connection between the furnace, which must be allowed to tilt about 5.degree. toward the slag door and 10.degree. toward the tapping spout, and the preheater which is stationary.
The charging car functions as a combustion chamber with a burner of variable air-fuel ratio to control oxygen contained in off gas from the furnace. It can direct the furnace off gas to the combustion chamber or divert it to a by-pass. It increases the feeding rate of the scrap delivered by the preheater, spreading it and therefore increasing heat transfer. It decreases the impact of the heavier scrap when reaching the steel bath by decreasing the length of the chute.
The vibrating pan follows the furnace when tilting minus 5.degree. and plus 10.degree., allowing constant power on during the slagging and tapping procedures. The vibrating pan oscillates continuously at low speed to improve the scrap feed distribution when the furnace is in the vertical position during most of the tap-to-tap cycle.
The charging, or connecting, car can be disengaged from the furnace when the furnace is drained at the end of the campaign, or when the furnace operates in conventional (non-continuous) mode, so that the furnace off gas by-passes the preheater directly to a gas cleaner.
The charging car apparatus is movable into and out of the operative position, and is preferably track mounted.